Microparticles prepared using an ionic liquid

ABSTRACT

Microparticles comprising at least one active agent embedded within a biocompatible, biodegradable polymeric matrix, wherein said microparticles are prepared with an ionic liquid.

FIELD OF THE INVENTION

The present invention provides microparticles comprising at least oneactive agent embedded within a biocompatible, biodegradable polymericmatrix, wherein said microparticles are prepared with an ionic liquid.

BACKGROUND OF THE INVENTION

It is advantageous to prepare microparticles having a biologicallyactive or pharmaceutically active agent within a biocompatible,biodegradable polymer to provide sustained or delayed release of theactive agent. Typically, the microparticles are prepared by dissolving,dispersing or emulsifying an active agent in a solvent containing apolymer. The solvent is then removed from the microparticles.

U.S. Pat. No. 6,228,398 describes microparticles containing a bioactiveagent in a polymer matrix. The microparticles are prepared using asolvent which exhibits a high vapor pressure to ensure that the finalsolvent extraction step can be carried out quickly. Suitable solventsare listed as ethyl acetate, dichloromethane, chloroform and propylenecarbonate.

Bodmeier et al., Int. J. Pharmaceutics, Vol. 43, pp. 179-186 (1988),describes the preparation of microparticles containing quinidine orquinidine sulfate as the active agent and poly(D,L-lactide) as thebinder using a variety of solvents including methylene chloride,chloroform and benzene as well as mixtures of methylene chloride and awater miscible liquid, such as acetone, ethyl acetate, methanol,dimethylsulfoxide, chloroform or benzene to enhance drug content.

Beck et al., Biol. Reprod., Vol. 28, pp. 186-195 (1983), describes aprocess for encapsulating norethisterone in a copolymer of D,L-lactideand glycolide by dissolving both the co-polymer and the norethisteronein a mixture of chloroform and acetone that is added to a stirred coldaqueous solution of polyvinyl alcohol to form an emulsion and thevolatile solvents removed under reduced pressure to yield microcapsules.

All of the microencapsulation processes described above employ volatilesolvents. In many instances, the solvents are halogenated hydrocarbons,such as chloroform and methylene chloride, which are especiallyundesirable because of their general toxicity, possible carcinogenicactivity and environmental concern.

We have now found after exhaustive testing that it is possible to makemicroparticles without using volatile solvents.

SUMMARY OF THE INVENTION

The invention provides microparticles comprising at least one activeagent embedded within a biocompatible, biodegradable polymeric matrix,wherein said microparticles are prepared with an ionic liquid.

According to another aspect the invention provides a method forpreparing microparticles comprising dissolving, dispersing oremulsifying an active agent in a biocompatible, biodegradable polymerand an ionic liquid, to form a mixture; and removing the ionic liquidfrom the mixture, thereby forming microparticles containing the activeagent embedded within a polymeric matrix.

Microparticles prepared according to the invention have the followingadvantages:

-   -   (i) an active agent or drug substance and a polymer which are        used to prepare the microparticles may co-dissolve in the ionic        liquid which may eliminate an emulsification or drug suspending        step in a process to prepare the microparticles;    -   (ii) the distribution of an active agent or drug substance in a        polymer matrix may be more homogeneous in the microparticles;    -   (iii) the microparticles are free from halogenated hydrocarbon        residues;    -   (iv) the microparticles are prepared essentially free of        volatile solvents since the ionic liquids have essentially no        vapor pressure;    -   (v) the particle size, shape, and density of the microparticles        may be controlled by the choice of ionic liquid;    -   (vi) an active agent and a polymer may be co-dissolved in the        ionic liquid; and    -   (vii) a peptide or protein co-dissolved with a polymer in the        ionic liquid may not undergo potentially devastating stress        conditions during emulsification or suspension of a        protein/water phase in a polymer/ionic liquid phase.

DESCRIPTION OF THE INVENTION

The microparticles of the invention comprising at least one active agentembedded within a biocompatible, biodegradable polymeric matrix areprepared with at least one ionic liquid. As used herein, the terms“microparticles” and “microspheres” include solid particles that containan active agent dispersed or dissolved within a biodegradable,biocompatible polymer that serves as the matrix of the particle. As usedherein, the term “biodegradable” means a material that should degrade bybodily processes to products readily disposable by the body and shouldnot accumulate in the body. The products of the biodegration should alsobe biocompatible with the body. As used herein, the term “biocompatible”means not toxic to the human body and is pharmaceutically acceptable.

The biodegradable, biocompatible polymer may be a synthetic polymer ornatural polymer. As used herein, “polymer” means at least one monomer isused in the polymerization, thus, “polymer” includes co-polymers,terpolymers, tetrapolymers, etc. The polymer may be cross-linked ornon-cross-linked. Preferably, the degree of cross-linking is less than5%, more preferably, less than 1%. Suitable polymers include thefollowing:

-   -   a) linear or branched polyesters which are linear chains        radiating from a polyol moiety, e.g., glucose;    -   b) polyesters, such as D-, L- or racemic polylactic acid,        polyglycolic acid, polyhydroxybutyric acid, polycaprolactone,        polyalkylene oxalate, polyalkylene glycol esters of acids of the        Kreb's cycle, e.g., citric acid cycle, and the like and        combinations thereof;    -   c) polymers of organic ethers, anhydrides, amides and        orthoesters    -   d) co-polymers of organic esters, ethers, anhydrides, amides,        and orthoesters by themselves or in combination with other        monomers; and    -   e) polyvinylalcohol.

Preferred examples of polymers which form the polymeric matrix includepoly(glycolic acid), poly(D,L-lactic acid), poly(L-lactic acid),co-polymers of the foregoing, poly(DL-lactide-co-glycolide)-glucose(PLG-Glu) and the like. Various commercially availablepoly(lactide-co-glycolide) materials (PLGA) may be used in the method ofthe present invention. For example, poly(D,L-lactic-co-glycolic acid) iscommercially available from Medisorb Technologies International L.P. Asuitable product commercially available from Medisorb is a 50:50 poly(D,L-lactic co-glycolic acid) known as MEDISORB® 50:50 DL. This producthas a mole percent composition of 50% lactide and 50% glycolide. Othersuitable commercially available products are MEDISORB® 65:35 DL, 75:25DL, 85:15 DL and poly(D,L-lactic acid) (D,1-PLA). Poly(D,L lacticacids), e.g. R202 which has a number average molecular weight ofapproximately 16000, and poly(lactide-co-glycolides) are commerciallyavailable from Boehringer Ingelheim under its Resomer mark, e.g., PLGA50:50, e.g. Resomer RG 502 which has a number average molecular weightof approximately 12000, PLGA 75:25, e.g. Resomer RG 752 which has anumber average molecular weight of approximately 16000, D,1-PLA, e.g.Resomer RG 206, and poly (DL-lactide-co-glycolide), e.g. RG 505 whichhas a number average molecular weight of approximately 80000. PLG-GLUmay have a number average molecular weight of approximately 55200. Othersuitable commercially available products are from Birmingham Polymers.These co-polymers are available in a wide range of molecular weights andratios of lactic acid to glycolic acid.

The most preferred polymer for use in preparing the microparticles ofthe invention is the copolymer poly(D,L-lactide-co-glycolide). It ispreferred that the molar ratio of lactide to glycolide in such aco-polymer be in the range of from about 85:15 to about 50:50.

The molecular weight of the polymer should be high enough to form afilm, preferably from about 5,000 daltons to about 500,000 daltons.However, since the properties of the film are also partially dependenton the particular polymer being used, it is difficult to specify anappropriate molecular weight range for all polymers. The molecularweight of a polymer may also effect the biodegradation rate of thepolymer. By an appropriate selection of polymer and other variables,such as process conditions, excipients, loading of active agent, andwater content, microparticles can be made which exhibit diffusionalrelease and/or biodegradation release properties.

The active agent is dispersed or dissolved in the polymeric matrix ofthe microparticles. Any active agent may be used. Example of activeagents include, but are not limited to, peptides or proteins, hormones,analgesics, anti-migraine agents, ant-coagulant agents, narcoticantagonists, chelating agents, anti-anginal agents, chemotherapy agents,sedatives, anti-neoplastics, prostaglandins and anti-diuretic agents,drug compounds actng on the central nervous system, such as cerebralstimulants, e.g., methylphenidate; pain management active agents;alkaloids, such as opiates, e.g., morphine; cardiovascular drugs, suchas nitrates; and agents for treating rheumatic conditions. It is furtherappreciated that the active agents include, but are not limited to,proteins or peptides, such as insulin, calcitonin, calcitoningene-regulating protein, parathyroid hormone, GLP-1, atrial natriureticprotein, colony-stimulating factor, GM-CSF, betaseron, erythropoietin,interferons such as alpha-,beta- or gamma-interferon, human growthhormone, octreotide, somatropin, somatotropin, somastostatin,insulin-like growth factor (somatornedins), luteinizing hormonereleasing hormone, tissue plasminogen activator, growth hormonereleasing hormone, oxytocin, estradiol, growth hormones, leuprolideacetate, factor VIII, interleukins, such as interleukin-2, 3, 6, and 14,and analogues and antagonists thereof; analgesics, such as fentanyl,sufentanil, butorphanol, buprenorphine, levorphanol, morphine,hydromorphone, hydrocodone, oxymorphone, methadone, lidocaine,bupivacaine, diclofenac, naproxen, paverin and analogues thereof;anti-migraine agents, such as sumatriptan, ergot alkaloids and analoguesthereof; anti-coagulant agents, such as heparin, hirudin and analoguesthereof; anti-emetic agents, such as scopolamine, ondansetron,domperidone, metoclopramide and analogues thereof; cardiovascularagents, anti-hypertensive agents and vasodilators, such as diltiazem,clonidine, nifedipine, verapamil, isosorbide-5-mononitrate, organicnitrates, agents used in treatment of heart disorders and analoguesthereof; sedatives, such as benzodiazepines, phenothiozines andanalogues thereof; chelating agents; anti-diuretic agents, such asdesmopressin, vasopressin and analogues thereof; anti-anginal agents,such as nitroglycerine and analogues thereof; anti-neoplastics, such asfluorouracil, bleomycin and analogues thereof; prostaglandins andanalogues thereof; and chemotherapy agents, such as vincristine andanalogues thereof. The microparticles may contain a combination ofactive agents. For example, microparticles which contain at least twoactive agents may be desirable for combination therapies.

The loading of microparticles with active agent may be detected byUV/Vis spectroscopy and/or gel electrophoresis (native PAGE) and/or orHigh Pressure Liquid Chromatography (HPLC).

The amount of active agent depends on the type of active agent and thecondition to be treated. Preferably, the active agent is present in anamount of from about 0.1 to about 90 weight percent, based on the totalweight of the polymeric matrix. More preferably, the active agent ispresent in an amount of from about 2 to about 75 weight percent. Mostpreferably, in the case where the active agent is a protein, peptide, orhormone, the amount of active agent in the microparticles is from about1 to about 30 weight percent, preferably 1-20 weight percent, morepreferably 1-10 weight percent, and most preferably about 5 weightpercent, based on the total weight of the polymeric matrix.

In addition to the active agent, the microparticles may contain anenhancer compound or a sensitiser compound, in order to modify thebioavailability or therapeutic effect of the active agent. As usedherein, “enhancer” refers to a compound which is capable of enhancingthe absorption and/or bioavailability of an active agent. Enhancersinclude, but are not limited to, medium chain fatty acids; salts,esters, ethers and derivatives thereof, including glycerides andtriglycerides; non-ionic surfactants such as those that can be preparedby reacting ethylene oxide with a fatty acid, a fatty alcohol, analkylphenol or a sorbitan or glycerol fatty acid ester; cytochrome P450inhibitors, P-glycoprotein inhibitors and the like; and mixtures of twoor more enhancers.

Ionic liquids are characterized by a positively charged cation and anegatively charged anion. Generally, any molten salt or mixture ofmolten salts is considered an ionic liquid. Ionic liquids typically haveessentially no vapor pressure, good heat transfer characteristics, arestable over a wide temperature range, and are capable of dissolving awide range of material in high concentrations. As used herein,“essentially no vapor pressure” means that the ionic liquid exhibits avapor pressure of less than about 1 mm/Hg at 25° C., preferably lessthan about 0.1 mm/Hg at 25° C.

With respect to the type of ionic liquid, a wide variety ofpossibilities exist. However, the preferred ionic liquids are liquid atrelatively low temperatures, for example, below the melting point of thecompound. Preferably, the ionic liquid has a melting point of less than250° C., more preferably less than 100° C. Most preferably, the ionicliquid has a melting point of less than 30° C. and is a liquid at roomtemperature. It Is within the scope of the invention to prepare an ionicliquid having any number of desirable properties, e.g. an ionic liquidthat dissolves a specific polymer which is used to preparemicroparticles.

With regard to viscosity of the ionic liquid, it is important that theviscosity of the ionic liquid not be too high to prevent a homogeneoussolution or dispersion of the active agent in the ionic liquid.Preferably, the ionic liquid has a viscosity of less than 500 centipoise(cP), more preferably, less than 300 cP, and most preferably less than100 cP, as determined at 25° C. The cation present in the ionic liquidcan be a single species or a plurality of different species. Both ofthese embodiments are intended to be embraced, unless otherwisespecified, by the use of the singular expression “cation”. The cationsof the ionic liquid include organic and inorganic cations. Examples ofcations include quaternary nitrogen-containing cations, phosphoniumcations and sulfonium cations.

The quaternary nitrogen-containing cations are not particularly limitedand embrace cyclic, aliphatic, and aromatic quaternarynitrogen-containing cations. Preferably, the quaternarynitrogen-containing cation is an n-alkyl pyridinium, a dialkylimidazolium or an alkylammonium of the formula R′_(4-X)NH_(X), wherein Xis 0-3 and each R′ is independently an alkyl group having 1-18 carbonatoms. It is believed that unsymmetrical cations can provide for lowermelting temperatures. The phosphonium cations are not particularlylimited and embrace cyclic, aliphatic and aromatic phosphonium cations.Preferably, the phosphonium cations include those of the formulaR″_(4-X)PH_(X), wherein X is 0-3, and each R″ is an alkyl or aryl group,such as an alkyl group having 1-18 carbon atoms or a phenyl group. Thesulfonium cations are not particularly limited and embrace cyclic,aliphatic and aromatic sulfonium cations. Preferably, the sulfoniumcations include those of the formula R′″_(3-X)SH_(X), wherein X is 0-2and each R′″ is an alkyl or aryl group, such as an alkyl group having1-18 carbon atoms or a phenyl group. Preferred cations include1-hexylpyridinium, ammonium, imidazolium, 1-ethyl-3-methylimidazolium,1-butyl-3-methylimidazolium, phosphonium and N-butylpyridinium.

The anion used in the ionic liquid is not particularly limited andincludes organic and inorganic anions. Generally the anion is derivedfrom an acid, especially a Lewis acid. The anions are typically metalhalides as described in more detail below, boron or phosphorusfluorides, alkylsulfonates including fluorinated alkyl sulfonates, suchas nonafluorobutanesulfonate; and carboxylic acid anions, such astrifluoroacetate and heptafluorobutanoate. The anion is preferably Cl⁻,Br⁻, NO₂ ⁻, NO₃ ⁻, AlCl₄ ⁻, BF₄ ⁻, PF₆ ⁻, CF₃COO⁻, CF₃SO₃ ⁻,(CF₃SO₂)₂N⁻, OAc⁻, CuCl₃ ⁻, GaBr₄ ⁻, GaCl₄ ⁻, SbF₆ ⁻ and CH₃SO₄.

Examples of ionic liquids include, but are not limited to, imidazoliumsalts, pyridium salts, ammonium salts, phosphonium salts and sulphoniumsalts. Preferred imidazolium salts have formula (I)

wherein

-   -   R¹ and R² are independently selected from the group consisting        of a C₁-C₁₈ aliphatic group and a C₄-C₁₈ aromatic group; and    -   A⁻ is an anion.

Preferably, R¹ and R² are independently selected from the groupconsisting of methyl, ethyl, propyl and butyl.

Preferred ammonium salts have formula (II)

wherein

-   -   R³, R⁴, R⁵ and R⁶ are independently selected from the group        consisting of a C₁-C₁₈ aliphatic group and a C₄-C₁₈ aromatic        group; and    -   A⁻ is an anion.

Preferably, R³, R⁴, R⁵ and R⁶ are independently selected from the groupconsisting of ethyl, propyl and butyl.

Preferred phosphonium salts have formula (III)

wherein

-   -   R⁷, R⁸, R⁹ and R¹⁰ are independently selected from the group        consisting of a C₁-C₁₈ aliphatic group and a C₄-C₁₈ aromatic        group; and    -   A⁻ is an anion.

Preferably, R⁷, R⁸, R⁹ and R¹⁰ are independently selected from the groupconsisting of ethyl and butyl.

Preferred pyridinium salts have formula (IV)

wherein

-   -   R¹¹ is selected from the group consisting of a C₁-C₁₈ aliphatic        group and a C₄-C₁₈ aromatic group; and    -   A⁻ is an anion.

Preferably R¹¹ is ethyl or butyl.

Specific examples of ionic liquids include, but are not limited to,1-butyl-3-methylimidazolium hexafluorophosphate,1-hexyl-3-methylimidazolium hexafluorophosphate,1-octyl-3-methylimidazolium hexafluorophosphate,1-decyl-3-methylimidazolium hexafluorophosphate,1-dodecyl-3-methylimidazolium hexafluorophosphate,1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulphonyl)-imidate,1-hexyl-3-methylimidazolium bis((trifluoromethyl)sulphonyl)amide,1-hexylpyridinium tetrafluoroborate, 1-octylpyridiniumtetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate,1-methy-3-ethyl imidazolium chloride, 1-ethyl-3-butyl imidazoliumchloride, 1-methy-3-butyl imidazolium chloride, 1-methy-3-butylimidazolium bromide, 1-methy-3-propyl imidazolium chloride,1-methy-3-hexyl imidazolium chloride, 1-methy-3-octyl imidazoliumchloride, 1-methy-3-decyl imidazolium chloride, 1-methy-3-dodecylimidazolium chloride, 1-methy-3-hexadecyl imidazolium chloride,1-methy-3-octadecyl imidazolium chloride, 1-methy-3-octadecylimidazolium chloride, ethyl pyridinium bromide, ethyl pyridiniumchloride, ethylene pyridinium dibromide, ethylene pyridinium dichloride,butyl pyridinium chloride, and benzyl pyridinium bromide.

Preferred ionic liquids are1-ethyl-3-methyl-imidazolium-trifluoroacetate,1-butyl-3-methyl-imidazolium-trifluoroacetate,1-ethyl-3-methyl-imidazolium-trifluoroacetate,1-butyl-3-methyl-imidazolium-hexafluoro-phosphate,1-octyl-3-methyl-imidazolium hexafluorophosphate,1-hexyl-3-methy-imidazolium hexafluorophosphate,1-butyl-3-methyl-imidazolium hexafluorophosphate,1-butyl-3-methyl-imidazolium tetrafluoroborate,1-ethyl-3-methyl-imidazolium-tetrafluoroborate,1-octyl-3-methyl-imidazolium-bromid,1-ethyl-3-methyl-imadazolium-trifluorosulfonate,1-butyl-3-methyl-imidazolium-trifluorosulfonate,1-butyl-3-methyl-imidazoliumtrifluoromethanesulfonate, 1-ethyl-3-methyl-imidazoliumtrifluoromethanesulfonate, and 1-ethyl-3-methyl-imidazoliumbis-(trifluoromethanesulfonyl)-imidate. Most preferably, the ionicliquid is selected from 1-ethyl-3-methyl-imidazolium-trifluorosulfonate,1-octyl-3-methyl-imidazolium hexafluorophosphate and1-hexyl-3-methyl-imidazolium hexafluorophosphate. A combination of ionicliquids may also be used.

In one embodiment of the invention, the microparticles are prepared by(i) dissolving or dispersing an active agent in a biocompatible,biodegradable polymer; (ii) dissolving the polymer containing the activeagent in an ionic liquid; and (iii) removing the ionic liquid to formmicroparticles, e.g. by washing the microparticles.

In another embodiment of the invention, the microparticles are preparedby (i)′ dissolving or dispersing an active agent in an ionic liquid;(ii)′ dissolving the ionic liquid containing the active agent in abiocompatible, biodegradable polymer; and (iii)′ removing the ionicliquid to form microparticles, e.g. by washing the microparticles.

In a further embodiment of the invention, the microparticles areprepared by (i)″ dissolving or dispersing an active agent in abiocompatible, biodegradable polymer and an ionic liquid to form amixture; (ii)″ adding a solvent and at least one surfactant to themixture; and (iii)″ removing the ionic liquid to form microparticles,e.g. by washing the microparticles.

In a further embodiment of the invention, the microparticles areprepared by (i)′″ dissolving or dispersing a biodegradable polymer in anionic liquid; (ii)′″ emulsification of the resulting solution in alipophilic phase; (iii)′″ adding a solution of an active agent to theemulsion to form microparticles and (iv)′″ removing the ionic liquide.g. by washing the microparticles.

Examples of surfactants include:

-   -   1) reaction products of a natural or hydrogenated castor oil and        ethylene oxide. The natural or hydrogenated castor oil may be        reacted with ethylene oxide in a molar ratio of from about 1:35        to about 1:60, with optional removal of the polyethyleneglycol        component from the products. Various such surfactants are        commercially available. The polyethyleneglycol-hydrogenated        castor oils available under the trademark CREMOPHOR are        especially suitable. Particularly suitable are CREMOPHOR RH 40,        which has a saponification number of about 50 to 60, an acid        number less than about 1, a water content (Fischer) less than        about 2%, an n_(D) ⁶⁰ of about 1.453 to 1.457 and an HLB of        about 14 to 16; and CREMOPHOR RH 60, which has a saponification        number of about 40 to 50, an acid number less than about 1, an        iodine number of less than about 1, a water content (Fischer) of        about 4.5 to 5.5%, an n_(D) ²⁵ of about 1.453 to 1.457 and an        HLB of about 15 to 17. An especially preferred product of this        class is CREMOPHOR RH40. Also suitable are polyethyleneglycol        castor oils such as that available under the trade name        CREMOPHOR EL, which has a molecular weight (by steam osmometry)        of about 1630, a saponification number of about 65 to 70, an        acid number of about 2, an iodine number of about 28 to 32 and        an n_(D) ²⁵ of about 1.471.        -   Similar or identical products which may also be used are            available under the trademarks NIKKOL (e.g. NIKKOL HCO-40            and HCO-60), MAPEG (e.g. MAPEG CO-40h), INCROCAS (e.g.            INCROCAS 40), and TAGAT (for example            polyoxyethylene-glycerol-fatty acid esters e.g. TAGAT RH 40;            and TAGAT TO, a polyoxyethylene-glycerol-trioleate having a            HLB value of 11.3; TAGAT TO is preferred). These surfactants            are further described in Fiedler, H. P. “Lexikon der            Hilfsstoffe für Pharmazie, Kosmetik und angrenzende            Gebiete”, Editio Cantor, D-7960 Aulendorf, 4th revised and            expanded edition (1996).    -   2) Polyoxyethylene-sorbitan-fatty acid esters, also called        polysorbates, for example mono- and tri-lauryl, palmityl,        stearyl and oleyl esters of the type known and commercially        available under the trademark TWEEN (Fiedler, loc.cit.,        p.1300-1304) including the products TWEEN        -   20 [polyoxyethylene(20)sorbitanmonolaurate],        -   21 (polyoxyethylene(4)sorbitanmonolaurate],        -   40 [polyoxyethylene(20)sorbitanmonopalmitate],        -   60 [polyoxyethylene(20)sorbitanmonostearate],        -   65 [polyoxyethylene(20)sorbitantristearate],        -   80 [polyoxyethylene(20)sorbitanmonooleate],        -   81 [polyoxyethylene(5)sorbitanmonooleate],        -   85 [polyoxyethylene(20)sorbitantrioleate].        -   Especially preferred products of this class are TWEEN 40 and            TWEEN 80.    -   3) Polyoxyethylene fatty acid esters, for example        polyoxyethylene stearic acid esters of the type known and        commercially available under the trademark MYRJ (Fiedler, loc.        cit., p.834-835). An especially preferred product of this class        is MYRJ 52 having a D²⁵ of about 1.1., a melting point of about        40 to 44° C., an HLB value of about 16.9., an acid value of        about 0 to 1 and a saponification no. of about 25 to 35.    -   4) Polyoxyethylene-polyoxypropylene co-polymers and block        co-polymers, for example of the type known and commercially        available under the trademark PLURONIC, EMKALYX and POLOXAMER        (Fiedler, loc. cit., p. 959). An especially preferred product of        this class is PLURONIC F68, having a melting point of about        52° C. and a molecular weight of about 6800 to 8975. A further        preferred product of this class is POLOXAMER 188.    -   5) Dioctylsulfosuccinate or di-[2-ethylhexyl]-succinate        (Fiedler, loc. cit. p.107-108).    -   6) Phospholipids, in particular lecithins (Fiedler, loc. cit. p.        943-944). Suitable lecithins include, in particular, soybean        lecithins.    -   7) Propylene glycol mono- and di-fatty acid esters such as        propylene glycol dicaprylate (also known and commercially        available under the trademark MIGLYOL 840), propylene glycol        dilaurate, propylene glycol hydroxystearate, propylene glycol        isostearate, propylene glycol laurate, propylene glycol        ricinoleate, propylene glycol stearate and so forth (Fiedler,        loc. cit. p. 808-809).    -   8) Polyoxyethylene alkyl ethers such as those commercially        available under the trademark BRIJ, e.g., Brij 92V, Brij 93 and        Brij 35.    -   9) Tocopherol esters, e.g., tocopheryl acetate and tocopheryl        acid succinate.    -   10) Docusate salts, e.g., dioctylsulfosuccinate or related        compounds, such as di-[2-ethylhexyl]-succinate (Fiedler, loc.        cit., p. 107-108).

A combination of surfactants may also be used.

Examples of solvents include: alkyl acetates, e.g. linear or branchedC₁₋₆ alkyl acetates, such as ethyl acetate, isopropyl acetate, and butylacetate; lower alkyl alcohols, e.g. linear or branched C₁₋₆ alkylalcohols such as methanol, ethanol, isopropanol, and butanol; aliphaticC₆₋₁₂ hydrocarbons, e.g. isooctane and n-heptane; aromatic hydrocarbonssuch as toluene, benzene; dialkyl ketones, e.g. acetone, methyl isobutylketone; acetonitrile; dialkyl ethers, e.g. diisopropyl ether anddiethylene ether; polyvinyl alcohol. A combination of solvents may alsobe used.

Examples of lipophilic phases e.g. lipophilic components, include:liquid paraffins (Fiedler loc. cit., p. 1141), silicon oils e.g.dimethicone (Fiedler loc. cit., p. 465), mixtures of middle-chaintriglycerides e.g. Miglyol 812® (Fiedler loc. cit., p. 1008) and oleicacid oleoyl esters e.g. Cetiol® (Fiedler loc. cit., p. 337). Acombination of lipophilic components may be used.

Prior to administration to a patient, the microparticles may besuspended in an acceptable pharmaceutical liquid vehicle. Thepharmaceutical liquid vehicle may optionally contain thickeners such ascarboxymethyl cellulose, etc., surfactants, such as polyoxyethylenesorbitan monooleate, polysorbate 20; and polyoxyalkylene derivatives ofpropylene glycol, etc., and/or isotonicity agents, such as sugars,salts, etc.

The microparticles can be mixed by size or by type so as to provide forthe delivery of active agent to a patient in a multiphasic manner and/orin a manner that provides different active agents to the patient atdifferent times, or a mixture of active agents at the same time.

The microparticles may vary in size, ranging from submicron tomillimeter diameters. Preferably, the average particle size of themicroparticles is from 1-500 microns, more preferably 10-200 microns,e.g. about 20 to about 40, e.g. about 30 microns. The microparticles mayshow a rough surface.

The amount of active agent, for example, peptide, present in themicroparticles depends on a number of factors. Such factors include, butare not limited to, the following: the desired daily release dosage, theloading capacity within the polymer, physical-chemical properties aswater solubility, the desired time of delivery, and polymer properties,e.g., degradation time and molecular weight. The exact amount of activeagent may be ascertained by loading experiments, in vitro and in vivodissolution rates and pharmacokinetic trials. Preferably, themicroparticles contain an active agent in an amount from 0.1-90 weightpercent (wt %), based on the weight of the polymeric matrix, morepreferably 2-75 wt %.

The release time of the active agent from the microparticle may be fromone or two weeks to about 12 months.

The following non-limiting examples illustrate further aspects of theinvention.

EXAMPLE 1

A) Preparation of Bromocryptine Mesylate Microparticles

Bromocryptine mesylate, 3 mg is dissolved and/or dispersed inpoly(D,L-lactid) R202, 15 mg. This combination is dissolved in 1 ml of1-ethyl-3-methyl-imidazolium-trifluorsulfonate and stored in acentrifuge tube. A lipophilic phase is prepared which contained paraffinand Brij 92V which is commercially available from Uniquema Everberg, asan emulsifier. The phases are emulsified with an IKA Vibrofix VF1Electronic high shear homogenizer. To the resulting emulsion, smallamounts of water is added step wise under furtherhomogenization/emulsification. Polyvinyl alcohol was added to theemulsion. Water is added to the emulsion, and the emulsion iscentrifuged yielding microparticles having a diameter of from 1 to 20microns.

Example 1A is repeated except that1-ethyl-3-methyl-imidazolium-trifluorsulfonate is replaced by the sameamount of 1-octyl-3-methyl-imidazolium hexafluorophosphate or1-hexyl-3-methyl-imidazolium hexafluorophosphate.

The process described in Example 1A may be up scaled e.g. 1000 fold.

B) Preparation of Bromocryptine Mesylate Microparticles

Bromocryptine mesylate, 3 mg is dissolved and/or dispersed inpoly(D,L-lactid) R202, 15 mg. This combination is dissolved in 1 ml of1-ethyl-3-methyl-imidazolium-trifluorsulfonate. A lipophilic phase isprepared which contained paraffin and BriJ 93 which is commerciallyavailable from Uniquema Everberg, as an emulsifier. The phases areemulsified with an IKAMAG® RCT magnetic stirrer. To the resultingemulsion, small amounts of water are added step wise under furtherhomogenization/emulsification. Polyvinyl alcohol was added to the water.The resulting suspension/emulsion is put In a centrifuge tube alreadycontaining 3 ml water and is centrifuged yielding microparticles havinga diameter of from 25 to 40 microns.

Example 1 B is repeated except that1-ethyl-3-methyl-imidazolium-trifluorsulfonate is replaced by the sameamount of 1-octyl-3-methyl-imidazolium hexafluorophosphate or1-hexyl-3-methyl-imidazolium hexafluorophosphate.

The process described in Example 1B may be up scaled e.g. 1000 fold.

EXAMPLE 2

Preparation of BSA Microparticles:

25 mg poly(D,L-lactid) R202 are dissolved in 0.5 ml of1-ethyl-3-methyl-imidazolium-trifluorsulfonate. This solution isemulsified in 4.5 ml liquid paraffin using an IKAMAG® RCT magneticstirrer. To stabilize the resulting emulsion 1% Brij 93 was added to theliquid paraffin. An aqueous solution of 50 mg/ml bovine albumin fractionV is prepared. 200 μl of this solution are added step wise under furtherhomogenization/emulsification. The resulting suspension/emulsion is putin a centrifuge tube already containing 5 ml water and is centrifugedyielding microparticles having a diameter of from 25 to 40 microns.

Example 2 is repeated except that1-ethyl-3-methyl-imidazolium-trifluorsulfonate is replaced by the sameamount of 1-octyl-3-methyl-imidazolium hexafluorophosphate or1-hexyl-3-methyl-imidazolium hexafluorophosphate.

The process described in Example 2 may be up scaled e.g. 1000 fold.

The Encapsulation of BSA is Shown by UV/Vis Spectroscopy andGel-electrophoresis (Native PAGE).

EXAMPLE 3

Preparation of Unloaded Microparticles:

Poly(D,L-lactid) R202, 15 mg is dissolved in 1 ml of1-ethyl-3-methyl-imidazolium-trifluorsulfonate. A lipophilic phase isprepared which contained paraffin and Brij 93 which is commerciallyavailable from Uniquema Everberg, as an emulsifier. The phases areemulsified with an IKAMAG® RCT magnetic stirrer. To the resultingemulsion, small amounts of water are added step wise under furtherhomogenization/emulsification. Polyvinyl alcohol was added to the water.The resulting suspension/emulsion is put in a centrifuge tube alreadycontaining 3 ml water and is centrifuged yielding microparticles havinga diameter of from 25 to 40 microns.

Example 3 is repeated except that1-ethyl-3-methyl-imidazolium-trifluorsulfonate is replaced by the sameamount of 1-octyl-3-methyl-imidazolium hexafluorophosphate or1-hexyl-3-methyl-imidazolium hexafluorophosphate.

The process described in Example 3 may be up scaled e.g. 1000 fold.

Microparticles prepared according to the invention have the followingadvantages:

-   -   (i) an active agent or drug substance and a polymer which are        used to prepare the microparticles may co-dissolve in the ionic        liquid which may eliminate an emulsification or drug suspending        step in a process to prepare the microparticles;    -   (ii) the distribution of an active agent or drug substance in a        polymer matrix may be more homogeneous in the microparticles;    -   (iii) the microparticles are free from halogenated hydrocarbon        residues;    -   (iv) the microparticles are prepared essentially free of        volatile solvents since the ionic liquids have essentially no        vapor pressure;    -   (v) the particle size, shape, and density of the microparticles        may be controlled by the choice of ionic liquid;    -   (vi) an active agent and a polymer may be co-dissolved in the        ionic liquid; and    -   (vii) a peptide or protein co-dissolved with a polymer in the        ionic liquid may not undergo potentially devastating stress        conditions during emulsification or suspension of a        protein/water phase in a polymer/ionic liquid phase.

While the invention has been described with particular reference tocertain embodiments thereof, it will be understood that changes andmodifications may be made by those of ordinary skill within the scopeand spirit of the following claims:

1. Microparticles comprising at least one active agent embedded within abiocompatible, biodegradable polymeric matrix, wherein saidmicroparticles are prepared with an ionic liquid.
 2. The microparticlesaccording to claim 1 wherein the ionic liquid has essentially no vaporpressure.
 3. The microparticles according to claim 5 wherein the ionicliquid has a vapor pressure of less than about 1 mm/Hg at 25° C.
 4. Themicroparticles according to claim 1 wherein the ionic liquid is selectedfrom the group consisting of: an imidazolium salt, pyridium salt,ammonium salt, phosphonium salt and sulphonium salt.
 5. Themicroparticles according to claim 1 wherein the ionic liquid is selectedfrom the group consisting of: 1-butyl-3-methylimidazoliumhexafluorophosphate, 1-hexyl-3-methylimidazolium hexafluorophosphate,1-octyl-3-methylimidazolium hexafluorophosphate,1-decyl-3-methylimidazolium hexafluorophosphate,1-dodecyl-3-methylimidazolium hexafluorophosphate,1-ethyl-3-methyl-imidazolium-trifluorosulfonate,1-butyl-3-methyl-imidazolium-trifluorosulfonate,1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulphonyl)-imidate,1-hexyl-3-methylimidazolium bis((trifluoromethyl)sulphonyl)amide,1-ethyl-3-methyl-imidazolium-trifluoroacetate,1-butyl-3-methyl-imidazolium-trifluoroacetate,1-ethyl-3-methyl-imidazolium-tetrafluoroborate, 1-hexylpyridiniumtetrafluoroborate, 1-octylpyridinium tetrafluoroborate,1-butyl-3-methylimidazolium tetrafluoroborate, 1-methy-3-ethylimidazolium chloride, 1-ethyl-3-butyl imidazolium chloride,1-methy-3-butyl imidazolium chloride, 1-methy-3-butyl imidazoliumbromide, 1-octyl-3-methyl-imidazolium-bromide, 1-methy-3-propylimidazolium chloride, 1-methy-3-hexyl imidazolium chloride,1-methy-3-octyl imidazolium chloride, 1-methy-3-decyl imidazoliumchloride, 1-methy-3-dodecyl imidazolium chloride, 1-methy-3-hexadecylimidazolium chloride, 1-methy-3-octadecyl imidazolium chloride,1-methy-3-octadecyl imidazolium chloride, ethyl pyridinium bromide,ethyl pyridinium chloride, ethylene pyridinium dibromide, ethylenepyridinium dichloride, butyl pyridinium chloride, benzyl pyridiniumbromide, and mixtures thereof.
 6. The microparticles according to claim1 wherein the polymer is a co-polymer of poly(glycolic acid) andpoly(D,L-lactic acid).
 7. The microparticles according to claim 1wherein the active agent is selected from the group consisting of apeptide, protein, hormone, analgesic, anti-migraine agent,anti-coagulant agent, narcotic antagonist, chelating agent, anti-anginalagent, chemotherapy agent, sedative, anti-neoplastic, prostaglandin andantidiuretic agent, cerebral stimulant, pain management agent,antalkaloid, cardiovascular drug and agent for treating rheumaticcondition.
 8. The microparticles according to claim 7 wherein thepeptide or protein is selected from the group consisting of insulin,calcitonin, calcitonin gene-regulating protein, parathyroid hormone,GLP-1, atrial natriuretic protein, colony-stimulating factor, GM-CSF,betaseron, erythropoietin, α-interferon, β-interferon, γ-interferon,human growth hormone, octreotide, somatropin, somatotropin,somastostatin, somatomedins, luteinizing hormone releasing hormone,tissue plasminogen activator, growth hormone releasing hormone,oxytocin, estradiol, growth hormones, leuprolide acetate, factor VIII,interleukin-2, interleukin-3, interleukin-6, interleukin-14, andanalogues and antagonists thereof.
 9. Microparticles comprising at leastone active agent embedded within a biocompatible, biodegradablepolymeric matrix, and at least one ionic liquid.
 10. A method forpreparing microparticles comprising (i) dissolving or dispersing anactive agent in a biocompatible, biodegradable polymer; (ii) dissolvingthe polymer containing the active agent in an ionic liquid; and (iii)removing the ionic liquid to form microparticles.
 11. A method forpreparing microparticles comprising (i)′ dissolving or dispersing anactive agent in an ionic liquid; (ii)′ dissolving the ionic liquidcontaining the active agent in a biocompatible, biodegradable polymer;and (iii)′ removing the ionic liquid to form microparticles.
 12. Amethod for preparing microparticles comprising (i)″ dissolving ordispersing an active agent in a biocompatible, biodegradable polymer andan ionic liquid to form a mixture; (ii)″ adding a solvent and at leastone surfactant to the mixture; and (iii)″ removing the ionic liquid toform microparticles.
 13. A method for preparing microparticlescomprising (i)′″ dissolving or dispersing a biodegradable polymer in anionic liquid; (ii)′″ emulsification of the resulting solution in alipophilic phase; (iii)′″ adding a solution of an active agent to theemulsion to form microparticles, and (iv)′″ removing the ionic liquid.14. The method according to claim 12 wherein the surfactant is selectedfrom the group consisting of a reaction products of a natural orhydrogenated castor oil and ethylene oxide,polyoxyethylene-sorbitan-fatty acid esters, polyoxyethylene fatty acidesters, polyoxyethylene-polyoxypropylene co-polymers and blockco-polymers, dioctylsulfosuccinate or di-[2-ethylhexyl]-succinate,phospholipids, propylene glycol mono- and di-fatty acid esters,polyoxyethylene alkyl ethers, tocopherol esters, and docusate salts andcombinations thereof.
 15. The method according to claim 12 wherein thesolvent is selected from the group consisting of an alkyl acetate, loweralkyl alcohol, aliphatic C₆₋₁₂ hydrocarbon, aromatic hydrocarbon,dialkyl ketone, dialkyl ether, and combinations thereof.
 16. The methodaccording to claim 13 wherein the lipophilic phase is selected from thegroup consisting of liquid paraffins, silicon oils, mixtures ofmiddle-chain triglycerides, oleic acid oleoyl esters and combinationsthereof.